Telescopes have been used for hundreds of years to magnify the images of distant objects. In 1672, Sir Isaac Newton developed what was believed to be the first reflective telescope. This type of telescope has become known as a Newtonian telescope. One specific type of a Newtonian telescope is a Gregorian telescope. Gregorian telescopes may be used in applications where upright images are required and in applications that cannot tolerate strong optical aberration. Traditional Gregorian telescopes have a primary mirror and a secondary mirror, where the distance between the primary mirror and the secondary mirror is greater than the focal length of the primary mirror. Other types of telescopes may include, for example, those employing refractive, reflective or catadioptic systems.
One problem of such systems is encountered when large optical telescopes are deployed, for example, extra-terrestrially. A limiting factor in telescope design is the launch-vehicle capacity. Such large telescopes quickly meet the payload capacities of launch-vehicles. One solution to this problem was the use of sparse aperture telescopes. Alternatively, or in conjunction with a sparse aperture telescope, telescope arrays have also been used. These telescopes have just recently been realized and may be able to reduce the weight and size of the system below that for a fully-filled aperture system. Sparse aperture telescopes may be able to increase the effective diameter of an optical system while reducing the overall weight and stowable size of the system. Generally speaking, a sparse aperture system synthesizes the light received from a number of smaller apertures, known as sub-apertures that are phased to form a common image field. This configuration enables the increase of the effective aperture size, while avoiding the difficulties associated with manufacturing and transporting a large monolithic mirror.
An additional solution to the problems associated with large telescope designs is to segment the primary mirror of the telescope. Segmenting the primary mirror of the telescope permits telescopes with larger aperture dimensions. Sparse apertures can be used to maximize resolving power given a mass constraint. However, for such systems, a significant fraction of the mass budget is typically devoted to the superstructure necessary to achieve the required levels of stability and rigidity. This is due to the axial extent of the system, or “depth”. This depth is usually much larger than the aperture extent. A reduction in the depth of a sparse aperture system may be achieved by employing an array of telescopes, but the optics required to optically combine the telescopes to image at a single image plane is very complex and may result in field-of-regard and throughput limitations.
What is needed is a telescope with a reduced depth to permit higher-powered telescopes to be carried by traditional launch-vehicles. Additionally, what is needed is a telescope that has a length measured in an axial direction that is substantially reduced as compared with traditional telescopes, while being configured with the same aperture size. Also, what is needed is a telescope that does not require complex optical systems for the combination of outputs from a number of telescopic systems.